Its star performers - the agency calls them 'the world's foremost speakers' - can command fees of up to £137,000 for a single engagement.

While Mrs Blair will not pull in fees at that level, industry insiders said she could expect up to $50,000 per engagement - almost £30,000 - from clients such as academic institutions.

The tour will have an additional benefit; dramatically raising Mrs Blair's profile among the Americans at the same time as her book The Goldfish Bowl, profiling Downing Street spouses, hits the shops.

Mrs Blair's surprise decision to take to the lecture circuit suggests she has abandoned her ambition to become a High Court judge.

That has never looked realistic since the Cheriegate row when she was caught out over her relationship with convicted Australian conman Peter Foster over the purchase of two flats in Bristol.

The lecture tour also suggests that the Blairs are beginning to plan for a life after Downing Street.

One acquaintance of Mrs Blair said that she believed they would 'make their fortune' in the U.S. when he ends his political career.

The Harry Walker Agency is thrilled with its latest signing. E-mailing key clients, it describes Mrs Blair as "the noted British attorney, human rights advocate and wife of Prime Minister Tony Blair".

It goes on: "Cherie Blair is a trailblazer in her professional life and a dedicated wife and mother in her private life. She is a highly respected international role model."

It also quotes the Prime Minister as saying he regards his wife as "an enormous source of strength and an extraordinary person in her own right. I never know how she manages with all the different things she does - the work, the family."

The agency says Mrs Blair will be available on October 26, 27 and 29, but suggests that she plans further forays on the U.S. speaking circuit.

"I know Cherie Blair would be a great success at your next event, so please contact me today for more information about her lecture topics, October schedule and future scheduling opportunities."

The speaking tour was confirmed by Mrs Blair's legal chambers, Matrix. A spokesman said: "Cherie is already speaking in the United States in October. It has been in her diary for some time.

"She has accepted an invitation from this organisation to speak while in the United States on subjects which are within her professional expertise.'

The Harry Walker Agency is known for demanding high fees for its star speakers. When the Parliamentary Press Gallery invited Bill Clinton to speak, the Walker Agency not only named a fee of $250,000, but asked for first-class round-trip expenses for Mr Clinton and two aides. The invitation was withdrawn.

The U.S. lecture tour is not the first time that Mrs Blair has sought to capitalise on her position as the Premier's wife.

Last year she created a furore by scooping up 68 items from a Melbourne supermarket after being invited to take 'a few things' as gifts.

She has also become notorious at party conferences for touring the exhibition stands and helping herself to soft toys and other freebies.

And with her husband she has enjoyed a string of free trips every year since arriving in Downing Street.

This summer, the Blairs are in the middle of a hat-trick of freebie holidays - at Sir Cliff Richard's Barbados mansion, Prince Girolomo Strozzi's Tuscan palace and the Sardinian retreat of Italian Premier Silvio Berlusconi.